Not able; not having sufficient strength, means, knowledge, skill, or the like; impotent; weak; helpless; incapable; -- now usually followed by an infinitive or an adverbial phrase; as, unable for work; unable to bear fatigue.
Is an indication report that the order, as given or when given, was unable to be executed. This can happen on a limit order where the market continues to trade at the limit price but there were other orders ahead of it on a time basis.
(usually followed by `to') lacking necessary physical or mental ability; "dyslexics are unable to learn to read adequately"; "the sun was unable to melt enough snow"